We own few Mustangs Fastbacks 1967 and 1968 ready to be build. Also own few rare S-code cars equipped from factory in 390cui engines. They are usually unmolested projects, in need of metal works. This is the best starting point.
Typical building time is around year. Usually we restore car to match 100% factory specification, with posibility of upgrade typical problems like power steering (we can use EPAS system), alternator (we can use one wire alternator), modern transmissions or suspension.